1. Technical Field
The present disclosure relates generally to the field of polyurea coatings and composites, and methods of making the same. More particularly, the present disclosure relates to the incorporation of siloxane polymers into two part polyurea elastomer coatings and composites.
2. Related Art
Polyurea are amine-containing terminated polyols reacted with isocyanates. Polyureas were developed in the 1980s for rapid process application of durable protective membranes for a myriad of products and technologies. Conventional polyurea coatings typically possess several characteristics that have made them desirable as a seamless membrane including fast, consistent reactivity and cure, moisture and temperature insensitivity during application, exceptional elastomeric quality, hydrolytically stability (i.e. low water absorption), high thermal stability, an auto catalytic nature, and non-emission of solvents or volatile organic compounds when applied. However, many characteristics of conventional polyureas are unfavorable and limit their use in many applications.
Conventional aromatic polyurea use mixtures of aromatic diamines such as diethyl toluene diamine and polyether amines reacted with a methylene diphenyl isocyanate (MDI) prepolymer. This material reacts rapidly to produce a polyurea, often in ten seconds or less. A conventional aliphatic polyurea can be made with aliphatic isocyanate reacted with aliphatic amines, such as commercially available products like Jefferamine T-403, D400, D2000, or NH 1220 from Huntsman and NH 1420 from Bayer. This reaction can be very fast with gel times of as little as 5 seconds. However, conventional aromatic and aliphatic polyureas are attacked by strong solvents such as xylene, toluene, acetone, low pH acids, and high pH caustics.
Another undesirable characteristic of conventional polyureas is that conventional polyureas possess poor adhesion properties. Specifically, the fast reaction times inherent in conventional polyureas cut short the time needed for a conventional polyurea to penetrate and adhere to its substrate. Commercial epoxy type resins have been used in place of conventional polyureas because they are slow to react but penetrate to give excellent adhesion and chemical resistance.
A further problem with conventional polyureas and epoxies is that they do not possess good color stability or UV resistance. Aromatic polyureas, due to their aromatic reactants, generally turn yellow or brown when exposed to ultraviolet (UV) light and oxygen. Since polyureas can be formulated in a variety of colors, this discoloration may adversely affects the intended finish color of the conventional polyurea coating, especially for outdoor application and with lighter colors.
Additionally, conventional polyurea coating tend to absorb liquids such as water, ethanol, or toluene, and over time, may distort and lose their tear strength. Furthermore, at lower temperatures, conventional polyureas can lose their flexibility and become brittle and subject to cracking.
Therefore, there is a need for a polyurea with a silicone backbone that would increase chemical resistance, UV stability, and temperature resistance.